1. Field of the Invention
The present invention relates to a disk drive such as a hard disk drive and a floppy disk drive using mainly a composite magnetic head with a thin film type wherein a write head and a read head are structured in a composite form.
2. Description of the Related Art
In the conventional magnetic disk drive, there is a disadvantage in which the performance of the recording and that of the reproducing cannot be suitably designed since recording and reproducing of signals are performed by the same head even if an access system of the head differs. As a technique for solving this problem, there is known a method for making the recording and the reproducing suitable independently by structuring the write head and the read head in a composite form. This type of the head is called as a composite head to distinguish from the conventional recording/reproducing common head.
A head which a magnetic force generating coil is combined into a ring-shaped core, which is designed such that a suitable signal recording can be performed as a recording head, is used (hereinafter called as an inductive head for convenience based on a reproducing principle through it is not suitable for a name of the write head). Also, an inductive head or a magnetoresistive head (hereinafter called as an MR head, and there is a case in which an MR head of composite type is simply called as an MR head) is used as a read head. Then, these heads are structured in a composite form (a case of the layer structure as in the thin film type is included), thereby the composite head is structured.
In consideration of the miniaturization of the future magnetic disk drive and inclination of high density thereof, it is desirable that there is used a composite head wherein there is provided such a head is superior to the conventional inductive head in sensitivity of reproducing, the MR head whose reproducing output has no relation with the relative speed of the head and the disk is used as a read head, and the read head and the write head of the inductive type are structured in a composite form.
In a small-sized disk drive, a rotary actuator is used since the structure is simpler than a linear actuator and there are advantages in terms of low cost, excellent vibration resistance, and low consumption of electric power, and so on (FIGS. 1A and 1B show one example of a magnetic disk drive of rotary actuator system).
The following explains a case in which the magnetic disk drive of the rotary actuator system using the composite head in which the write head and the read head are structured in a composite form (for example, a thin film magnetic head of composite type, which is structured by layering a thin film magnetic head of inductive type, serving as a write head, and MR head, serving as a read head). As shown in FIGS. 1A to 2, if the composite magnetic head is accessed in the range from an innermost track position to an outermost track by rotating an arm of the rotary actuator, misregistration is generated at a position of a recording track on the magnetic disk and a position of the read head by a skew angle .theta.. As shown in FIG. 2, an amount of track misregistration can be described by D.multidot.sin.theta.. D shows a space between a magnetic gap of the write head and that of the read head (FIG. 2 shows a case using the inductive head at both write and read operations, and central position of a reproducing element effect section is meant in the case of the MR head of FIGS. 1A and 1B, but hereinafter simply called as a magnetic gap as the similar meaning).
In the specification of the present invention, in order to visually easily understand the relationship between the head position and the magnetic disk rotating direction, as shown in FIG. 2, an area where the write head traces is called as a recording track, and an area where the read traces is called as a reproducing track. In contrast, an area on the magnetic disk for the recording/reproducing is originally performed is called a data track or simply as a track. In a case that the magnetic disk drive is structured in which the recording track and the reproducing track are conformed to each other when the positioning is performed at the central track (in a case that the width of the recording track and that of the reproducing track are different, the centers of both recording and reproducing tracks are conformed to each other, and in a case that the centers of both tracks deviate, an amount of misregistration is shown by a distance between both centers), the positional relationship between the recording track and reproducing track at each track position when the head is moved from the outermost circumference to the innermost circumference, and an inclination of the recording/reproducing gap are shown in FIGS. 3A to 3C. FIGS. 3A to 3C show the inclination of the recording/reproducing gap, and the gap therebetween is described wider than the actual case.
FIG. 4 shows an example of a format of the magnetic disk drive. At a head of each sector, there is provided an ID section where ID information of the sector (cylinder number, head number, presence or non-presence of defect depending, etc.) is recorded, it is needed that ID information be read before processing to a data area in any cases, that is, a case in which data is reproduced and a case in which data is recorded.
A mode is changed in order that the write head is on a data track at a write operation and the read head is on a data track at the write operation. In this case, if an offset amount of a voice coil motor (VCM) is finely adjusted so that a desired head flows the data track, the data section can be recorded/reproduced without deteriorating S/N. However, since the ID section is required to be read at both read and write operations, the following problem occurs. More specifically, it is extremely difficult to change the mode such that the write head is set to be on track after reproducing the ID section physically existing in the same sector by use of the reproducing head since the mode change must be instantaneously performed.
If the width of the recording head is sufficiently made wider to the width of the read head, the reproducing track can be surely included in the recording track. Due to this, ID information can be read without having deterioration of quality of a signal of the data section caused by the writing/reading head misregistration. However, this is not favorable in view of the point that a track density is increased.
"Track Density Constraints in the Application of MR Head Technology" IEEE TRANSACTION ON MAGNETICS, Vol. 28, No. 5, P. 2728, 1992 discloses the following two methods.
(1) The ID area and the data area are provided in a different physical sector; and PA1 (2) A plurality of ID (for reproducing and recording) is provided.
However, in the method (1), a through put of data access is lowered. In the method (2), though there is no description of the specific structure, it is described that the ID area is divided into odd tracks and even tracks, and a plurality of ID is provided.
FIG. 5 is a view showing an example having a plurality of ID areas. FIG. 6 is a view showing a method for recording a servo signal. According to FIG. 6, for example, servo information is written as shown by 1 to the final in accordance with head positions 1 to 5 at a servo write operation. Then, for example, the write head and the read head are controlled to be positioned to be at a center of the track at the write and read operations, respectively. According to FIG. 5, there is provided the structure in which each ID area to each track of the odd and even tracks is wider than the track, whereby ID information is correctly read. This structure is an effective method to solve the track misregistration. However, according to this method, since the servo write does not conform to the ID area of each track (that is, information is overwritten with a half pitch of the read head), it is required that ID information be written twice, and it takes much time to write ID information.
FIG. 7 is a view showing a general structure of the servo area.
Generally, the servo area has an address AGC area, an erased area, a track address code area, a burst AGC area, a positioning data area, and a gap section. The address AGC area controls a gain of an auto gain control (AGC) amplifier so as to standardize amplitude of a reproduced signal, and ensures the detection of the sequential erased area and the reproduction of the track address code area. The erased area recognizes the start of the servo area. An address in which the head exists is allotted to the track address code area. The burst AGC area adjusts the gain of the AGC amplifier so as to ensure extraction of positioning information from burst pattern data of the sequential positioning data area. The gap section absorbs of rotation jitter of the magnetic disk.
Generally, as shown in FIG. 8, the positioning data area of the hard disk drive in which the conventional inductive head is provided has a plurality of burst areas (in this example, A, B, C and D areas). In each burst area, a burst signal area where continuous data is recorded with the width Tp of the track pitch and an area erased in a DC manner are alternately provided in a direction of the width of the track. That is, the burst signal area and the erased area are provided as deviating in the width direction of the track.
A dash and dotted line of FIG. 8 shows a center of each center. In order to position the magnetic head at the center of the track, the position of the magnetic head is controlled such that a value of (a-b)/(a+b) is set to 0 from amplitude a of the reproduced signal sent from the burst area A and amplitude b of the reproduced signal sent from the burst area B.
The burst areas C and D are recorded a position at which differs a half pitch from the burst A and the burst B to obtain a good linearity even in a case that the magnetic head is presented in an area where the magnetic head crosses the adjacent two tracks (i.e., in a case of head position having wrong linearity obtained from position information generated by the signals of the burst A and the burst B).
In order to form the above-mentioned positioning data area, as shown in FIGS. 9A to 9C, the recording of the positioning data area is performed by feeding the magnetic head by a half of the track pitch Tp, and overwriting information on a base recording before the movement of the head to a portion, and adjusting the phases.
In the case that the positioning data area is recorded by use of the inductive recording MR reproducing composite head (hereinafter, referred to as a composite MR head), there is known that an edge bipolar charge directing in a direction of the width of the track is generated at both sides of the recording track. The similar phenomenon is generated when a DC erase is performed as shown FIG. 10A. FIG. 10B shows the structure of the write head section of the composite MR head. The magnetic gap is formed by a lower pole of the reproducing side and the upper pole of trailing side. In reproduction using the composite MR head, if the magnetic flux sent from the edge bipolar charge is fetched to the MR film of the MR head, there is a problem in which offset is generated in the reproduced signal in a DC manner.
According to the same method as the case using the conventional inductive head, as shown in FIG. 11A, in a case that the edge bipolar charge appears in the portion overwritten by the DC erase of positioning data, and the edge bipolar charge is reproduced by the composite MR head so as to obtain head positioning information, since the MR head obtains the reproduced signal at the position where the MR head crosses the edge of the burst area, the MR head is subjected to influence of the edge bipolar charge. Due to this, the reproduced signal of head positioning information has offset in the DC manner every burst area shown FIG. 11B.